Jellyfish invasion

This summer, nearly 30 years after the movie Jaws scared throngs of beachgoers out of the water, another marine menace is haunting the shallows. Considerably smaller than the great white shark that terrorized the fictional resort of Amity Island, this creature doesn't bite, but it can pack a nasty sting--and its numbers are on the rise.
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The blue planet

Indeed, quivering armadas of them--yes, jellyfish--have invaded coastlines worldwide, from Puget Sound and the Bering Sea to the Boston and Tokyo harbors. Huge swarms, or "smacks," have shut down fisheries in the Gulf of Alaska, Narragansett Bay, and the Black Sea. In the Philippines, an estimated 50 tons of the bobbing blobs caused a massive blackout--sparking rumors of a coup d'etat--when they were sucked into a power plant's cooling system.

What's behind the invasions? Marine scientists haven't yet solved the mystery, but increasingly they blame warming oceans, overharvesting of fish stocks, and the tons of fertilizer, sewage, and other nutrient-rich pollution fouling coastal waters.

Gobs of blobs. With the seas so vast and the network of scientists studying jellyfish blooms so small--fewer than 100 worldwide--researchers don't yet have a clear sense of the geographical extent of the problem. "But almost everywhere there are people looking," says Barbara Sullivan, a biological oceanographer at the University of Rhode Island's Graduate School of Oceanography, "they've found more."

Sullivan speculates that the rise of 2 to 3 degrees Celsius in winter and spring water temperatures in Narragansett Bay over the past three decades may explain the doubling of the comb jelly population. On a sultry afternoon recently on a stretch of beach in the town of Narragansett, glittering dragonflies darted along the mouth of the Narrow River estuary and warblers flitted around fragrant bayberry bushes and the pink blooms of swamp rose mallows. But with the water thick with fist-size, shimmering jellies, Sullivan wasn't recommending a dip. Although the jellies don't sting, she says, "it can be icky bumping into all those globs of gooey stuff."

Researchers working in the Chesapeake Bay have also seen a link between warming waters and booming numbers of jellies. Jennifer Purcell, a jellyfish ecologist who studied bay jellies for 17 years before relocating recently to Western Washington University's Shannon Point Marine Center, has found that the bay's ranks of comb jellies and sea nettles are especially high after hot, dry springs. Purcell and colleagues also have examined wintertime temperatures in the Chesapeake and the Black Sea, where a plague of comb jellies--introduced accidentally in ballast water two decades ago--has devastated fisheries. In both places they found that the gelatinous creatures are more abundant after warm winters.

Nutrient-rich pollution has probably also aided jelly populations in the bay and the Black Sea, suggests Purcell. Nitrate-laden fertilizers and sewage foster the growth of smaller varieties of algae, which, in turn, increase the numbers of smaller types of algae-grazing creatures. This increase gives jellies an advantage over fish in their competition for food because while fish are visual predators--and so prefer larger prey--jellies consume whatever drifts their way.